1. Bio-Contaminants & Food Webs
By: Patuxent Wildlife Research Center

2. Lesson 1 Review Points Using Science as Evidence
When science is used as evidence it is important to identify possible sources of bias.
Bias may be due to sampling bias or measurement bias.
Background of DDT
DDT is a pesticide used for mosquito control and pest control in agricultural crops.
DDT accumulation in some bird species resulted in death, nervous system damage, and reproductive failure.
As a result DDT was banned in the United States in
If students had difficulty with concepts from lesson one, review the examples from the previous day.
The answer to Review Questions 1 and 2 are on this slide.
Review Question 1: What are two sources of bias? 1) Sampling Bias 2) Measurement Bias
Review Question 2: What year was DDT banned in the United States? 1972 *

3. What are some sources of bias?
Applying the results of a study too broadly (generalizing)
Taking research results out of context
Not taking a random sample
Taking too small of a sample
Measurement error
Review Question 3: Name three sources of bias. Any of the five listed source of bias are acceptable. *

4. Lesson 2 Food Webs, Bioaccumulation, and Visualizing Data
The goal of lesson two is to introduce the concepts of bioaccumulation and biomagnification and their importance in the environment. Additionally, lesson two introduces students to the natural history of osprey and bald eagles in the context of food webs. Finally, students will be encouraged to visualize what type of graph they can expect with various datasets. *

5. Positive Aspects DDT
Insecticide used to kill pests and damaging insects in Agriculture
Commonly kills off mosquitoes, and has been used to help fight malaria.

6. What kind of damage can DDT cause to birds?

7. In the body of an animal, DDT is changed (metabolized) to DDE
In the body of an animal, DDT is changed (metabolized) to DDE. DDE dissolves in fat, not in water, and is stored in fatty tissues. Thus, DDE tends to remain in the body and can cause several problems.

8. DDE: Kinds of Damage
Reproductive failure (in birds- eggshell thinning)
Immune system problems
Nervous system damage
Death
☺ Students will be asked to list some of the damage caused by DDE on their worksheets. *

9. How does DDT move into lakes, streams and oceans?

10. After DDT is applied, some DDT volatizes, some remains on the plant, and some washes off the plant into the soil, eventually making its way to a a stream, river, or lake.
The DDT that remains on the leaves of plants may be ingested by primary consumers such as insects and rodents.
DDT that has washed into a waterbody, remains in the sediment or is consumed by bottom-feeding organisms or absorbed by fish gills and skin.
After DDT is applied, some DDT residue remains on the plant material and some washes off the plant into the soil eventually making its way to a body of water. The DDT that remains on the leaves of plants is taken up by primary consumers such as insects and rodents. As for the DDT that has washed into a stream, river or lake, it enters the food chain through consumption by bottom-feeding fish or through absorption by fish gills and skin. *

11. Is DDT still used today?

12. DDT is still used in some countries for insect control on crops.
YES
DDT is still used in some countries for insect control on crops.
In countries where mosquitoes carry malaria, DDT is currently used for mosquito control.
In some countries, DDT is still applied to crops or to wetlands for general insect and mosquito control. After DDT is applied, some DDT residue remains on the plant material and some washes off the plant into the soil eventually making its way to a body of water. The DDT that remains on the leaves of plants is taken up by primary consumers such as insects and rodents. As for the DDT that has washed into a stream, river or lake, it enters the food chain through consumption by bottom-feeding fish or through absorption by fish gills and skin. *

13. What is a Food Web?
At this point it may seem that a completely new topic is being introduced. To transition to the explanation of food webs, ask students how the toxicity of DDE is related to food webs. *

14. Food Web = A summary of the feeding relationships within an ecological community.
Osprey
Sucker
Trout
In lesson three the students will work with an osprey dataset. To familiarize students with some of feeding habits of osprey,the example food web focuses on osprey. For additional information about osprey refer to the osprey information sheet.
The osprey is often mistakenly called the fish hawk or fish eagle. Historically, ospreys were reported as numerous, nesting in forested areas near water because they favored dead trees or trees with flat or dead tops. Unlike most birds of prey, osprey are tolerant of human activities and will build nests on almost any suitable structure close to water and with an abundant supply of fish. Ospreys are able to catch fish by hovering, and then plunging three feet into the water to capture fish. Their dense oily feathers make them suited to repel water and quickly regain flight.
USGS Osprey in Oregon and the Pacific Northwest. USGS FS
☺ Students will be asked to define food web on their worksheet.
Silverside
Bay Shrimp
Water Plants
Plankton
ORGANIC DEBRIS *

15. Food Chain = One thread of the food web
Osprey
Large Mouth Bass
This is the same picture of food web but with one chain highlighted. It is assumed that most students are familiar with the basic concept of food webs and food chains. If food webs and food chains are new material, please refer to the suggested reading site for additional information. The following website also has additional information about food webs:
Crayfish
ORGANIC DEBRIS *

16. Cast of Food Web Characters
Tertiary Consumers – Animals that eat animals that eat animals
Secondary Consumers – Animals that eat animals that eat plants
Primary Consumers – Animals that eat plants
Primary Producers – Plants and Phytoplankton: organisms using the sun for energy
☺ Students have a copy of this pyramid on their worksheet and are to identify primary producers, primary consumers, secondary consumers, and tertiary consumers. *

17. Why is food web knowledge important for understanding the impact of DDT on ospreys and eagles?

18. Ospreys and eagles are tertiary consumers and this makes them particularly vulnerable to DDT because of bioaccumulation and biomagnification.
☺ The students will be asked to write down the definitions to bioaccumulation and biomagnification. Both terms will be define in the upcoming slides. *

19. What is bioaccumulation?

20. Bioaccumulation = the accumulation of a contaminant or toxin in or on an organism from all sources (e.g., food, water, air). An increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.
Chemicals that are soluble in fat, like DDE, particularly tend to bioaccumulate compared to those soluble in water. Chemicals that are soluble water are removed from the body in urine, whereas those soluble in fat, do not have a means to leave the body and remain in tissue. *

21. What is biomagnification?

22. Biomagnification = the increase in concentration of toxin as it passes through successive levels of the food webDDE accumulates at higher levels in organisms that are higher in the food chain

23. Biomagnification of a DDE in Aquatic Environment
Level
Amount of DDE in Tissue
Tertiary Consumer µg/g ww
(fish eating birds)
Secondary Consumers µg/g ww
(large fish)
Primary Consumers
(small fish)
This is an example of actual concentrations of DDT as it passes through the heron food chain. It is important that the students notice the units in which DDT is measured and to become familiar with the relative amount of DDT that accumulates in organisms of different trophic levels. Students will also be given another example using osprey to demonstrate this point.
There are several factors that contribute to the problem of bioaccumulation and biomagnification in aquatic environments. When DDT is applied it runs off into water and collects in lakes, streams, wetlands and other bodies of water. Fish are then exposed to DDT through consumption of organic debris on the floor of a water body and/or through their gills when it is suspended in water. Thus, water dwelling creatures are at higher risk of bioaccumulating DDE.
µg/g ww
Primary Producers
(algae and aquatic plants)
0.04 µg/g ww *

24. Considering biomagnification, how could DDE harm an osprey?

25. DDE Concentration Osprey 3-76 µg/g ww Large Mouth Bass 1-2 µg/g ww
Osprey Food Web
DDE Concentration
Osprey
3-76 µg/g ww
Large Mouth Bass
1-2 µg/g ww
Osprey are at the top of the aquatic food chain, and are thus exposed to many pollutants found in the environment. Toxic chemicals are present in water, air, sediments, and aquatic biota throughout osprey breeding and wintering ranges. Many of these contaminants bioconcentrate from water passed through fish gills, and bioaccumulate in the fish from their food. The efficient transfer of chemicals from food to consumer through two or more trophic levels results in biomagnification, a systematic increase in tissue residue concentrations from one trophic level to another.
USGS Osprey in Oregon and the Pacific Northwest. USGS FS
☺ Students will be asked to fill in the food chain given here and the relative concentrations of DDE.
µg/g ww
Crayfish
Plant material and algae
0.04 µg/g ww *

26. Units of Measurement
1 gram = 1000 milligrams (mg) = 1,000,000 micrograms (µg)
microgram (µg) = one millionth of a gram
To describe concentrations: µg/g = number of micrograms
(of toxin) per gram (of tissue)
2 µg/g DDE in egg content means there is 2 parts of DDE in 1,000,000 parts of an egg contents
ww or wet weight refers to the fresh weight of animal tissue.
dw or dry weight refers to the weight of animal tissue after it has been dried in an 65°C oven to remove all the water.
This slide will give a quick introduction to the units of measurement that are used for measuring concentrations. Micrograms per gram is in several of the slides in lesson 2 and wet weight and dry weight are in lesson 3 and 4.
For additional information about units of measurements the following website is a useful reference: *

27. The Effects of DDE on Reproduction
Species
Effect on Reproduction
DDE: Critical Concentration (measured in egg contents)
Bald Eagle
None
< 3µg/g 1
Failure
16 µg/g 1
Osprey
17.6 µg/g 2
Because both bald eagles and osprey are at the top of the food chain, the DDE biomagnifies in their tissue and this results in eggshell thinning. This slide combines results from two different studies measuring the concentration of DDE in eggs and comparing it to the reproductive success of bald eagles and osprey.
This slide shows the DDE concentration level that results in total reproductive failure, and this level of DDE concentration would result in an immediate local extinction. In other words, if bald eagles or ospreys were exposed to the above levels of DDT, within one generation there would be a local extinction. It is important to note that levels between three and 16 µg/g impair reproduction. Intermediate levels of DDT concentration would result in a slow decline in the bald eagle and osprey populations, and this would likely lead to an eventual extinction.
Wiemeyer, S.N. et al., Organochlorine pesticide, polychlorobiphenyl, and mercury residues in bald eagles, , and their relationship to shell thinning and reproduction. Arch. Environ. Contam. Toxicol., 13, 529.
Johnson, D.R. et al., DDT and PCB levels in Lake Coeur d’Alene, Idaho osprey eggs, Bull. Environ. Contam. Toxicol., 13, 401. *

28. High levels of DDE cause the female ospreys to lay eggs with thin eggshells. Thin eggshells have a greater chance of breaking, leading to embryo death. With high levels of DDE, female ospreys can also lay eggs that contain high enough concentration of DDE to prevent embryo development.
☺ Students have fill-in-the-blank questions to answer questions about this slide. It is important that students understand that high levels of DDE result in female osprey to lay thin eggs with thin eggshells. *

29. How is the impact of DDE on osprey and eagle reproduction measured?
In Lesson 3 and Lesson 4 students will be working with real data. In order for students to have a clear picture of how and why data was collected, the next slide introduces the data collection method. *

30. One Method for Measuring the Impact of DDE on Osprey Reproduction
Collect eggs from abandoned osprey nests.
Measure the thickness of the eggshells.
Measure the amount of DDE in the egg.
Determine the association between eggshell thickness and DDE residue.

31. Visualizing the Data
The last part of the lecture focuses on data visualization. This exercise is included to encourage students to start thinking about how graphs of different types of datasets may appear. For advanced students,teachers can first put up the question and then let students draw out the graph on their worksheets. For students less comfortable with graphing, teachers may want to guide students through the graphing process using the following steps:
Drawing the axes on the board.
As a class, determine the labels of the axes.
As a class, work out the first graph. *

32. If increased DDE concentrations causes increased eggshell thinning, how would you draw a graph showing the relationship between eggshell thinning and DDE concentration?

33. The above graph depicts data where eggshells with higher levels of DDE concentration are thinner.*

34. If DDE has no impact on eggshell thickness, what relationship would you expect to see between DDE levels and eggshell thickness?

35. This graph depicts data where regardless of the concentration of DDE, eggshells have the same thickness. *

36. If increased levels of DDE are associated with increased eggshell thickness, how would you make a graph showing the relationship between eggshell thickness and DDE concentration? *

37. This graph shows a situation where eggshells with higher concentrations of DDE are thicker than those with lower concentrations of DDE. *

38. DDE reduces reproductive rates at moderate concentrations
DDE reduces reproductive rates at moderate concentrations. At high concentrations it causes total reproductive failure.
How would you make a graph showing the relationship between DDE concentration and reproductive success?

39. At moderate DDE concentration there is slightly lower reproductive success than at low DDE concentrations and at a certain high concentration of DDE there is total reproductive failure. *